Numerous types of electrical actuators have been known in the art for use in electrical relays for switching electrical contacts dependent upon the existence of a particular condition. Such actuators typically incorporate an electromagnet with the state of energization of the coil controlling the state of the actuator. If one contact is closed when the actuator coil is de-energized, and another contact is closed when the coil is energized, the relay contacts are said to be double-throw. If contact is made only when the coil is energized and the connection is open when the coil is de-energized, then the relay contacts are single-throw. In the case where the actuator contacts return to a particular position in the absence of coil energization, the relay is known as side-stable. The invention herein relates particularly to a double-throw, side-stable electromagnetic actuator.
Double-throw actuators have typically used springs to hold the contacts closed when the coil is de-energized. In such a case, however, the spring force must be overcome when the coil is energized and the actuator and relay are switched. As a point of fact, it can be shown that an actuator for double-throw contacts must perform three and one-half times the work required for single-throw contacts when the contacts that are closed with the coil de-energized are held closed with spring force. As is well known in the art, the size and weight of the electromagnetic actuator must increase as the required work increases. To provide an electromagnetic actuator of physically small dimension and light weight, means other than springs must be utilized for holding the normally closed contacts or those contacts which are held closed in the absence of coil energization.
A permanent magnet has been used in the industry to replace springs. However, in present actuator magnetic structures employing permanent magnets, a magnetic bias or an air gap, or both, must be used to achieve the proper operation.
It has been known in electrical actuators that it is necessary to have a wide separation between the pick-up and drop-out force curves. It has further become known that the load curves of those forces which must be overcome to effect switching, such as springs, air gaps, and the like, should fall between the pickup and drop-out curves of the actuators. At this point, it should be understood that the pick-up current is that current applied to the coil of the electromagnet of the actuator to achieve switching. In similar fashion, the drop-out current is that current which, when applied to the coil, will be insufficient to hold the contacts in their activated state. As is known in the art, the pick-up and drop-out force curves plot such currents as a function of the switching force operating on the actuator armature, and the gap between the armature and its closed contact position. As just discussed, proper electromagnetic actuator design requires that the load forces of springs, air gaps, electrical contacts, and the like fall between the pick-up and dropout force curves such that the actuator will have both a rapid and positive response to applied voltages.
In the prior art, without the cost of size and weight, it has been impossible to obtain a significant separation between the pick-up and drop-out force curves of a double-throw electromagnetic actuator with the load curves lying therebetween.
While the prior art has taught various types of electromagnetic actuators, and particularly those incorporating a combination of permanent magnets and electromagnets, none have achieved the benefits of the invention as will hereinafter be described. For purposes of background, the following United States Patents are acknowledged as being of interest only: U.S. Pat. Nos. 1,689,946; 2,941,130; 3,284,798; 3,317,871; 3,559,129; 3,621,419; 3,775,715; 3,968,470; 4,015,174; 4,237,439; and 4,286,244.